Surge tanks are designed to control pressure surges or transients in pipelines, which are created when the flow of the fluid is abruptly changed. Pressure transients can be either positive or negative and are potentially destructive and may result in damage to piping, pumps, instruments, fittings, or other system components.
Surge tanks have been used for years as a means for controlling pressure transients. Some surge tanks employ a bladder design and are well known having applications within various industries, including fire protection systems, municipal water and sewage systems, desalination facilities, fuel systems, and chemical and petrochemical facilities.
During a pump start up, for example, a high transient of pressure is created at the pump discharge. Installation of a bladder surge tank at the pump discharge absorbs the fluid from the pump until the fluid achieves steady state velocity, then the surge tank discharges the fluid into the system to balance the pressure and eliminate the pressure transient. Pressure transients may also be created where there is a sudden and abrupt cessation of liquid flow, hereto, bladder surge tanks can eliminate the pressure transient. Bladder surge tanks also have application as a deluge surge tank where the instantaneous discharge of fluid is required in, for example, fire protection systems.
Regardless of the application, the shape of the bladder during gas precharge or fluid discharge is not totally controllable. In systems where the flow rate exceeds 500 gpm, the bladder may actually seal the tank's fluid inlet/outlet opening during liquid discharge and prevent the tank from emptying its liquid contents. To prevent this, some bladder surge tank manufacturers have placed a wire screen in the tank's inlet/outlet opening. Unfortunately, such a screen actually impedes the liquid flow and is not totally effective in preventing the bladder from blocking the tank's fluid inlet/outlet opening during fluid discharge.
Where there is a sudden flow of fluid into a bladder surge tank, the force of the incoming fluid is concentrated and assumes the shape of the tank's fluid inlet/outlet opening. Such a column of fluid and its associated force is directed towards that portion of the bladder directly above the tank's inlet/outlet opening and can cause damage to the bladder.
There remains a need for a bladder surge tank that eliminates the likelihood of having the bladder block the tank's inlet/outlet opening during fluid discharge and thus interfere with the flow of fluid out of the bladder surge tank. There also remains a need for a bladder surge tank that can redirect the fluid entering the bladder surge tank in a more uniform pattern, thus reducing the possibility of bladder damage from the force of the incoming fluid.
Further, in applications where the system fluid being handled is sewage, e.g., comprising a mixture of liquid and solid components, there is a need to provide a bladder surge tank that can provide the desired degree of surge protection without plugging or fouling, which would impair the ability to provide surge protection, and which would require frequent maintenance to ensure proper operation.